The drug discovery process is currently undergoing a fundamental revolution as it embraces “functional genomics”, that is, high throughput genome- or gene-based biology. This approach as a means to identify genes and gene products as therapeutic targets is rapidly superseding earlier approaches based on “positional cloning”. A phenotype, that is a biological function or genetic disease, would be identified and this would then be tracked back to the responsible gene, based on its genetic map position.
Functional genomics relies heavily on high-throughput DNA sequencing technologies and the various tools of bioinformatics to identify gene sequences of potential interest from the many molecular biology databases now available. There is a continuing need to identify and characterise further genes and their related polypeptides/proteins, as targets for drug discovery. Recent advances in this area are mainly driven by applying advanced screening systems with focus to the function of newly identified proteins. Interesting application for this type of screens are whithin the field of tumor apoptosis.
Apoptosis of tumor cells can be blocked e.g. by mutations in crucial genes like those frequently found in the well known p53 tumor suppressor protein. Another mechanism that blocks apoptosis is caused by the protein family of “inhibitors of apoptosis” (IAPs), reviewed by Deveraux and Reed (Genes & Development 1999). One member of this family is encoded by the Survivin gene.
The strongest evidence for an IAP involvement in cancer is seen for Survivin (see review of Altieri and Marchisio, Laboratory Investigation 1999). Although not observed in adult differentiated tissue, Survivin becomes prominently expressed in transformed cell lines and in all of the most common human cancers of lung, colon, pancreas, prostate and breast, in vivo. Survivin is also found in approximately 50% of high-grade non-Hodgkin's lymphomas (centroblastic, immunoblastic), but not in low-grade lymphomas (lymphocytic). Survivin inhibits caspase activity and apoptosis induced by Fas (CD95), Bax, Caspases, and anti-cancer drugs.
In addition, Survivin is upregulated 40-fold at G2/M phase of the cell cycle and binds to mitotic spindles (micro-tubules), although its role at the spindle is still unclear. There might be a connected control of apoptosis and mitotic spindle checkpoint by Survivin. Disruption of Survivin-microtubule interactions results in loss of Survivin's anti-apoptosis function and increased caspase-3 activity. Survivin may counteract a default induction of apoptosis in G2/M phase. The overexpression of Survivin in cancer may overcome this apoptotic checkpoint and favour aberrant progression of transformed cells through mitosis (Fengzhi et al., Nature 1998). In this repect it is important to note that it was recently shown that Survivin initiates procaspase 3/p21 complex formation as a result of interaction with Cdk4 to resist Fas-mediated cell death (Suzuki et al., Oncogene 2000). SIP-1 may therefore be implicated in the known tumor-cell-escape from the immune system. The other biochemical mechanisms, besides its inhibitory binding to Caspases, by which Survivin might mediate its anti-apoptotic activity are currently unclear.
Therefore in this invention we have screened for potential ligands that interact with Survivin. 